Method of electrophoretic surface coating



Jan. 2, 1968 E. B. TANNER METHOD OF ELECTROPHORETIC SURFACE COATING Filed April 7, 1964 lnuenlor EDWARD BUTLER TANNE- y MUJHTUM H l 5 Attorney 5 United States Patent 3,361,658 METHOD OF ELECTROPHORETIC SURFACE CGATING Edward Butler Tanner, Hampton-in-Arden, England, assignor to Pinchin, Johnson & Associates Limited, London, England, a British company Filed Apr. 7, 1964, Ser. No. 358,003 Claims priority, application Great Britain, Apr. 10, 1963, 14,302/ 63 2 Claims. (Cl. 204--181) ABSTRACT OF THE DISCLOSURE Metal articles to be painted by electrodeposition are carried on a conveyor anode, the liquid paint is poured on to the conveyor in one or more unconfined streams and the cathode, for example a wire, to complete the electric circuit is located within the paint streams.

This invention relates to the electrode/position of surface coatings.

One important aspect of the invention is the coating of metal articles by electrodeposition from water-thinnable paint media based on water-soluble synthetic resins, but the invention is also aplicable to the electrodeposition of other media, for example natural or artificial rubber latices.

It is known to deposit coatings on articles by making the article to be coated one electrode of an electrical circuit, the article being immersed in a bath of the coating liquid with the container functioning as the other electrode or one or more separate electrodes being immersed also in the liquid.

T he specification of my application No. 285,234, filed June 4, 1963, now abandoned, describes such a process in which the paint medium used as the electrodeposition bath contains at least 1 percent by weight of an organic liquid having a water-solubility at 20 C. of not more than 5 percent, and preferably not more than 1 percent, by weight. Examples of such liquids mentioned in the specification are hydrocarbons, esters, ketones and higher alcohols.

The present invention is directed to a novel method of electrodepositing the coating and in accordance with this invention, the article to be coated is made one electrode, as in previous practice, and the coating liquid used is directed on to the article as one or more liquid streams in which the other electrode, which can conveniently take the form of a wire, is inserted.

For carrying out the process of this invention the li uid coating is contained within a vessel provided with one or more spouts so that the liquid can be poured out of the vessel in a corresponding number of streams. The vessel and spouts may conveniently be constructed of non-conducting materials. A wire, forming the cathode for example, is located within, and it necessary insulated from, each spout so that when the liquid is poured on to the anode article, the electrical circuit is completed by the stream of liquid between the wire and the article. With such a system, the coating builds up on the article until the article is insulated to such an extent that the electrical circuit is broken. I have obtained uniform coatings of water-thinnable paints on metal articles using a voltage of volts with a pouring distance of about half an inch.

In operating the process it is preferred to collect the liquid which is not electrodeposited and circulate it by a pump back to the vessel in a continuous manner. It is also preferred either to mount the articles on a moving carrier so that they move past stationary liquid streams or to move the streams past a series of stationary articles. After the articles have been provided with the coating, they are rinsed with water and stoved in the usual manner.

The invention is illustrated in the accompanying drawing which shows an apparatus employing a moving carrier. The liquid coating material is contained within a vessel 1 having a spout 2 near its lower end. Just below the tip of the spout 2 there is a moving metallic band 3 moving continuously round rollers 4, 5 on shafts 6 and 7 respectively, one of which is driven by means not shown. A metal wire 8 is mounted within the spout 2 and passes from the spout through an insulated bush 9 to an electric supply 19 and the circuit is completed by a wire 11 connected to the shaft 6 of roller 4. In operation, paint from vessel 1 passes as a stream via the spout 2 on to the moving band 3 thereby completing the electrical circuit to the band. As the articles to be coated, for example metal panels, only one of which 12 is shown, pass under the stream the panels, which act as electrodes by virtue of their contact with the band 3, become cotaed while excess paint drains away, is collected in a tank 13 and pumped back to the vessel 1 by pump 14 by way of a pipe 15.

Although only one pouring vessel 1 is shown, any number of similar vessels may be provided, for example transversely across a moving band. Instead of putting the articles on the band itself small metal articles such as screws may be placed in shallow containers constructed of metal wire and the containers put on the band in a manner similar to that shown for the panel 12. If the vessel 1 and spout 2 are made of insulating material the bush 9 is not necessary.

The method of coating according to this invention avoids need for complicated apparatus for painting small articles where separate assembly of each article as an individual electrode is not possible. In addition, once each article is coated with the paint it becomes insulated and excessive buildup of coatings is avoided.

The process of this invention may be used to apply the paints described in my application Ser. No. 285,234.

The present invention is illustrated by the following example in which an apparatus as shown in the drawing was used.

The wire 8 in spout 2 was connected to the negative pole of a 180 volt electrical supply and the positive pole of the supply was connected to the shaft 6. A paint having the same composition as that set out in Example 1 of my application Ser. No. 285,234 was circulated as described so that it was poured continuously on to metal plates on the band 3 at a distance of about half an inch (1.25 cm.) for two minutes.

The plates were then washed with water and stoved for half an hour at 325 to 350 F. The finished plates were provided with a smooth glossy coating of substantially uniform thickness.

What I claim is:

1. A method for coating small metal articles by electrodeposition from a fluid aqueous coating suspension which comprises placing said articles on a horizontally moving carrier, directing downwardly on said articles a stream of said suspension, said stream moving, in its downward course, in contact With an electrode; and establishing an electric circuit through said carrier, the articles to be coated, said fluid stream and said electrode.

2. The process claimed in claim 1 and comprising collecting excess coating suspension and recirculating said collected suspension.

References Cited UNITED STATES PATENTS 2,576,362 11/1951 Rimbach 204-300 5 2,843,596 7/1958 Hoffman 204299 3,020,224 2/ 1962 Blank et a1. 204300 3,219,571 11/1965 Parent et al. 204-299 3,230,162 1/1966 Gilchrist 204181 JOHN H. MACK, Primary Examiner.

10 T. TUFARIELLO, Assistant Examiner. 

